Pregnancy Calculators
Free due date and conception calculators. Estimate your EDD from LMP, conception date, or ultrasound scan. Track gestational age, trimester, and pregnancy milestones.
Pregnancy Calculators - Plan and Track Your Pregnancy
Whether you are trying to conceive or already pregnant, accurate date calculations help you plan appointments, understand your fertile window, and track gestational milestones. These calculators use standard obstetric methods (Naegele’s rule, luteal phase dating) used by obstetricians and midwives worldwide.
Four Pregnancy Calculators
Ovulation Calculator - Find your estimated ovulation date, 6-day fertile window, next period date, and estimated due date if conception occurs. Shows 3 upcoming cycle windows in a table. Uses LMP and average cycle length with the standard luteal-phase formula.
Due Date Calculator - Calculate your estimated due date (EDD) from last menstrual period (Naegele’s rule), conception date, or ultrasound scan. Adjusts for cycle length, shows current gestational age in weeks and days, trimester, and key pregnancy milestones.
Conception Calculator - Find your estimated conception date by working backwards from your due date (EDD minus 266 days), or forward from your last menstrual period (LMP + cycle length minus 14). Shows gestational age in weeks and days, trimester, fertile window, and days remaining to the due date.
Gestational Age Calculator - Calculate exact gestational age in weeks and days from your last menstrual period (LMP) or estimated due date (EDD). Shows trimester, estimated due date, conception date, days remaining, and your next key pregnancy milestone. Supports both LMP-based and EDD-based input modes.
Understanding Conception and Ovulation Timing
Conception occurs when a sperm successfully fertilizes an egg during ovulation. Ovulation typically happens 14 days before the next expected period, regardless of cycle length. Only the follicular phase (LMP to ovulation) varies between women; the luteal phase (ovulation to next period) is consistently 14 days. This is why cycle-length-adjusted due dates differ from the standard 28-day Naegele’s rule: the due date shifts by exactly the number of days your cycle differs from 28.
The fertile window spans 6 days: the 5 days before ovulation and ovulation day itself. Conception rates are highest (25-30% per day) on the two days immediately before ovulation and on ovulation day. Sperm viability of up to 5 days explains why sex earlier in the fertile window can still result in conception.
Frequently Asked Questions
How accurate are LMP-based conception date estimates?
LMP-based dating assumes regular cycles with ovulation on day (cycle length minus 14). For regular cycles, the estimate is accurate within plus or minus 3-5 days. For irregular cycles, an early ultrasound (8-12 weeks) is the gold standard, accurate within plus or minus 5 days. The Conception Calculator adjusts the due date for cycle lengths other than 28 days using the same logic.
What is the difference between gestational age and fetal age?
Gestational age counts from the first day of the LMP and is the measure used by all doctors and ultrasounds. Fetal age (embryonic age) counts from conception, which is typically 2 weeks after LMP. A pregnancy at week 10 gestational age is at week 8 of actual fetal development. Always use gestational age when communicating with healthcare providers.